Posted by Marc F Hult on September 19, 2005, 2:03 pm
On 19 Sep 2005 08:23:57 GMT, ddl@danlan.*com (Dan Lanciani) wrote in message
MFHult@nothydrologistnot.com (Marc F Hult) writes:
and even maybe even NCAA Division 1 and 2 ;-)
Yes. See the ASCII circuit diagram in my previous post and at the end of this
one. which I think makes this clear. Over-current protection is included.
Where do I find out about class T fuses ? Searching the 2005 draft NEC came up
blank. Why do I need them? Plain old Square D QO circuit breakers are UL'd to
Right. ABIK, it has changed and become more restrictive/ less useful. That was
Outdoor wiring low-voltage wiring was separated in the 2002(?). I haven't
pursued what the draft 2005 has to say. but I didn't stumble across anything
that clarified how to get from one t'other or made life easier.
Yes and maybe not :-)
Yes, from the perspective that you are analyzing the benefits as if the
installation is something to be commercialized -- which it is not. There is no
reason why a personal endeavor ("hobby") has to be practical, or cost effective.
Most of what I see folks doing in comp.home.automation (and perhaps the
cross-posted NGs too) would not meet those criteria. Perhaps we need to start a
Yes, from social reality that in a system with multiple, distributed components
that require electrical power, the conventional approach of providing that
energy with Class 2 wallwarts quickly becomes untenable. Spousal factor -- the
answer to "Can I put three _more_ wall warts over here so that the open-close
and tilt drapery motors and the controller can be powered?" is "No". So what
to do ? One part of the answer is distributed DC power in my case.
Yes, examining the assertion that 120VAC is always standard and low-voltage is
non-standard. To the extent that many of my objectives stem from, and are
ultimately directed at environmental monitoring, 120 AC is very much the
non-standard, not low-voltage. When was the last time you saw a AC-powered pH or
conductance meter? Or weather station? Or sampling pump, or ... My backyard is
750 feet of river front that we own and I monitor.
Yes, from the standpoint that you see "keeping lines separate" as a negative.
We separate AC lines one from another too. Why is this a problem? Why is it not
a design advantage to have independent systems? I can rip everything I've
installed out and the house and household would go on jist fine, albeit with
diminution of smart/automation functionality and emergency and aesthetic aspects
Yes, from the difference that you see having to use Chapter 3 materials as a
problem, whereas I see it as the cheapest way to get materials in many cases
anyway. The power of Home Depotizing as it were ..
Yes, recognizing that I already have a large supply of components for DIY.
Sometimes I build things just to convert "parts" into "devices" (in the spirit
of rec.home.automation ;-)
Yes, from the fact that the "inherent loss disadvantages of low voltage" is
eliminated completely by proportional increase in the cross-sectional areas of
conductors. There are, of course, advantages to higher voltages. We converted
our house in Spain from 110 to 220 3-phase which made conductors embedded in
solid masonry walls much more useful. But that is not the situation in my US
home. I am installing new conductors, and don't have to retrofit. The house is
184 years old and this is at least the fifth energy/lighting infrastructure
(Candle/lamp; coal gas lighting; knob and tube electrical; 1983 Romex
remodeling; 21st century HA )
And maybe *not* ;-) because you have excellent analytical abilities and apply
them diligently to a confusing set of facts, boundary conditions, circumstances
and regulations in a way that is very helpful to others (too).
I _greatly_ appreciate you helpful comments. You've helped to clarify, organize
and correct much.
Regards ... Marc
In ASCII, continuing from previous diagram:
28vdc -+->Circuit Breaker--->Dimmer module--->12vdc track UL w/remote xfmr
| (Art. 720 + 240) (Art 725.21 Class 1)
+->Circuit Breaker -------------> devices
| (Art. 720 + 240)
+----> DC-DC converter ----+---> device
(Art.725 Class 2) +---> device ground
14vdc -+----> DC-DC converter ----+---> device
| (Art.725 Class 2) +---> device ground
(Art 725.21 Class 1)
0 ----------------------------------> ground
(Art. 720 and 725 class 1)
Not shown are low-voltage outdoor lighting or telecomm.
Posted by Dan Lanciani on September 21, 2005, 5:09 am
MFHult@nothydrologistnot.com (Marc F Hult) writes:
[this is getting long, so big snip...]
| I wrote:
| >Perhaps. However, I just looked at the hookup instructions and it appears
| >that the outputs are directly paralleled with the battery bank, i.e., whatever
| >over-current protection the devices offer does not actually protect the load
| >side. That suggests that no matter the listing the output is going to have to
| >be treated like the output of any other battery bank which can deliver very
| >high current, requiring, e.g., (expensive) class T fuses. And of course, the
| >wiring at that point isn't even class 1. (I used to think that it could be
| >class 1 subpar (b) which goes to 600V with no power limitations, but that's
| >for signaling/control only...)
| Yes. See the ASCII circuit diagram in my previous post and at the end of this
| one. which I think makes this clear. Over-current protection is included.
Yes, you were clear. I was confused by the description on the manufacturer's
site. With all the talk of sophisticated over-current detection I thought the
supply had to interpose some electronics between the battery string and the
output. I guess the protection is just for the wires to the battery. :( In
case you care, I'm pretty sure that there do exist supplies that work the way
I thought these work.
| Where do I find out about class T fuses ?
A Google search seems to turn up quite a few hits. One thing I noticed is
that they aren't as absurdly expensive as I remembered...
| Searching the 2005 draft NEC came up
| blank. Why do I need them?
To be honest, I'm not sure you do. This came up some years ago when I
added a remote battery string to a UPS. To my annoyance I found that while
inexpensive 100A automotive fuses could be used for similar applications in
cars, boats, mobile homes, and even internally to said UPS and its packaged
expansion batteries, I had to use a class T fuse because I was running the
circuit in a building. This might have been a local issue and/or I might have
overreacted to some of the requirements. After getting the correct fuse I sort
of stopped looking for additional problems because, well, the box I was using
wasn't a listed battery enclosure and the UPS wasn't actually listed for
connection to anything but their packaged expansion batteries (though at least
the string I used fell within the allowable range of capacities) and so on... :)
| Plain old Square D QO circuit breakers are UL'd to
As I recall, a circuit breaker with the required DC arc interrupting capacity
(20kA?) and response time was even more expensive than the fuses. But since
a lot of this is listing politics rather than genuine engineering it's
certainly possible that a commodity device would have been acceptable and
I just missed it.
| >If they have added a genuine class 2 supply requirement
| >I would think that many of the existing landscape lighting transformers are
| >now out of spec since even the multi-output ones typically exceeded 100VA on
| >each output. It may be that there is now a specific (and different) type
| >of class 2 listing for such supplies that makes this all work out. There
| >is an unfortunate trend in this respect to make listings extremely
| >specific, thus thwarting non-standard or unanticipated custom assemblies.
| Right. ABIK, it has changed and become more restrictive/ less useful. That was
| my point.
| Outdoor wiring low-voltage wiring was separated in the 2002(?). I haven't
| pursued what the draft 2005 has to say. but I didn't stumble across anything
| that clarified how to get from one t'other or made life easier.
I just checked the Juno Flex 12 system for which I happen to have a catalog.
It's one of those exposed-conductor indoor low-voltage track systems. The
transformers go to 600VA per circuit, so I think even indoor systems are
going to have a problem with a class 2 supply requirement. Unless those
were never under 411 to begin with (like your tracks?).
| >Here's the problem I had when I looked at the whole low-voltage DC
| >idea a while back. Whether you classify your circuits under 720 or 725's
| >class 1 you still have to use the same Chapter 3 materials and methods that
| >you would use for line voltage circuits. Plus you have to keep the two
| >(or maybe all three) separate. Plus you have to deal with non-standard
| >(and thus more expensive) ancillary components like DC-rated switches and
| >fuses. Plus you have the inherent loss disadvantages of low voltage. As
| >far as I can tell, the only thing you gain under class 1 is the ability to
| >use No. 16 and 18 conductors, not that I'd want to. Am I missing something?
| Yes and maybe not :-)
| Yes, from the perspective that you are analyzing the benefits as if the
| installation is something to be commercialized -- which it is not.
I was really trying to frame some simpler questions. What is it that you
are allowed to do by remaining < 30V that you would not be allowed to do if
you used, say, 48V? Similarly for using DC instead of AC.
| Yes, from social reality that in a system with multiple, distributed components
| that require electrical power, the conventional approach of providing that
| energy with Class 2 wallwarts quickly becomes untenable. Spousal factor -- the
| answer to "Can I put three _more_ wall warts over here so that the open-close
| and tilt drapery motors and the controller can be powered?" is "No". So what
| to do ? One part of the answer is distributed DC power in my case.
Don't the DC/DC converters take up about as much space as the wall warts
they replace? Or do you have enough consumer devices that require neither
voltage conversion nor isolation nor class 2 current limitation that you come
Posted by Marc F Hult on September 25, 2005, 3:48 pm
On 21 Sep 2005 05:09:19 GMT, ddl@danlan.*com (Dan Lanciani) wrote in message
IOW, get back to the Q&A that might have transfer value to other folks.
Thank you ;-)
Allow me to assert that, side for legacy requirements for some thermostats
and HVAC controls, nearly all home automation/control/measurement electrical
power needs are intrinsically DC. (Air conditioning, heating, large motors
etc are beyond our scope here.)
The system I've described and shown in schematics consists in building blocks
in increments of nominal 12vdc (~13.8 vdc. One can easily add additional
voltages in series on _top_ of the 0-12-24vdc voltage, 80/60 amp
So I could create a 1.25 amp 48vdc supply with two 1.25amp 13.8vdc Powersonic
wall-wart chargers and two 7AH sealed lead cells (the most cost-effective
size) that I have on hand and move around for various projects. I have been
using this particular combination from this supplier for isolated power
supplies for environmental monitoring for at least 20 years.
This would provide a system with 0-12-24-36-48vdc at 80/60/1.25/1.25 amps
48vdc just doesn't happen to be needed in my case right now, which (based on
the devices I have) _does_ need ~40 amps at nominal 24vdc to power the DC
dimmers that I happen to use. Requirements of other folks will vary. Point is
that the approach is modular, and one can move things around as needs change,
which in a experimental/hobbyist environment, they inevitably do.
Recognize that if the battery bank weren't there, and aside from the
specific listing issue, the 80-amp 12vdc "tap" is Class 1-compliant so one
could partially "de-build" to reach a particular code goal/requirement should
it come to that.
Using a 40 amp instead of 60amp charger/supply would make the 24vdc tap also
Class 1 (same provisos).
No, in part because the DC-DC converters can be internal to the devices they
power. Compare the hodge-potch of wall-warts, power strips, surge protectors,
and local UPS's that conventionally are used to power a pc and associated
accoutrements with these:
(the 12vdc on the latter is pass-through, not regulated.
Which, *inside* an (eg) low-power PC such as VIA EPIA is smaller, more
energy efficient, has fewer connections to fail, and has longer battery
backup among other things.
A standard/conventional hermaphroditic connector for DC connectors are the
Anderson Powerpole series
which have been adopted by hams as informal quasi standard for Radio Amateur
Civil Emergency Service (RACES) among others
Purchased inexpensively here:
And recognize -- importantly! -- that the short back-up time on under-desk
UP's don't actually solve *anything* if the PC is supposed to stay up
permanently which is often the case in HA applications. So the conventional
under-desk AC-based tangled jumble fails and the almost invisible, internal
DC solution elegantly and dependably meets the needs.
Depending on the specific CPU requirements (part of this approach involves
getting real with what we actually need in terms of computational horsepower)
sufficient 5vdc and(or) 12vdc power may be available from the same DC-DC
converter to supply a router or other gizmo. If not, add another DC-DC
converter, perhaps within the same case, but certainly not on the wall or on
an AC power strip.
I think that you are asking whether I use devices that can use unregulated
nominal 12vdc or 24vdc. Yes. 12vdc devices abound. And this is a factor in my
purchasing decisions. It also prompts me to take the covers off devices to
see what their internal power supplies _really_ need.
Posted by Marc F Hult on September 25, 2005, 4:01 pm
On 21 Sep 2005 05:09:19 GMT, ddl@danlan.*com (Dan Lanciani) wrote in message
Let me tackle the 'AC' part here.
(We need to stick to comparing pomes (as in apples to pears) so large diesel
generators and other solutions beyond the modest ones previously implied are
beyond the scope of the solutions to be discussed here.)
I've recently discussed the aesthetic problem of "wall acne" in a thread in
comp.home.automation, so won't repeat that in this thread which is
cross-posted. Let it suffice that there are advantages to low voltage
distribution that are unrelated to the need for uninterrupted power. It is
the need for UPS that I address here.
Starting from the design objective of making power available ad infinitum,
not just for a few minutes to (eg) allow a computer to shut down. This
(necessarily, methinks) results in a _central_ UPS system the power from
which must be distributed as either DC or AC.
The DC supplies I've described provide about (60 x 14 + 80 x 14) =~ 2000
watts . Not coincidentally this is about what 15 amp (1800 watt) and 20 amp
(2400 watt) AC circuits can provide.
Noting that in the US, the National Electrical Code prohibits supplying a
(eg) a conventional wall outlet with less than a 15 amp source, it follows
that an AC UPS with the same capacity as the DC system I described must be on
a _single_ circuit There can be mo overcurrent protection between the panel
and the outlet less than 15 amps.
So in a NEC-compliant 15-20 amp distributed 120vac UPS wiring system, *every*
outlet goes dead if the trip point is exceeded.
1) After putting all the most important devices that should never be allowed
to go dead, a NEC-compliant AC system is vulnerable to someone plugging in a
vacuum cleaner during Saturday house cleaning, or to a space heater plugged
in during an emergency and shutting everything down. This is a recipe for
certain failure in my opinion. With the DC distribution system I've
described, over-voltatge protection can be used _ab_ libitum_ (although not
necessarily as effectively as desired -- 'nuther topic ;-)
2) Elsewhere in this thread, Dan correctly notes that the DC system described
requires running new/different wires. How does having power from a single ~
2000 watt UPS system distributed throughout the house obviate the need to
have new/different wires? As best I know, it doesn't.
3) From the efficiency standpoint, DC distribution also has the advantage
when efficiency is most needed, namely when running from batteries. In a DC
distributed system, the power used by (eg) PC goes through exactly one DC-DC
conversion (battery-> DC-DC converter inside PC). In a AC distributed
system, there are at least twice as many conversions with attendant decrease
in overall efficiency of battery utilization (battery--> DC_AC UPS -->
AC_DC_DC converter in computer).
Posted by Marc F Hult on September 25, 2005, 4:40 pm